Cardiovascular disease, including atherosclerosis, is the leading cause of death in the United States. One method for treating atherosclerosis and other forms of arterial lumen narrowing is percutaneous transluminal angioplasty, commonly referred to as “angioplasty” or “PTA,” or “PTCA” when performed in the coronary arteries. The objective in angioplasty is to restore adequate blood flow through the affected artery, which may be accomplished by inflating a balloon of a balloon catheter within the narrowed lumen of the artery to dilate the vessel.
The anatomy of arteries varies widely from patient to patient. Often a patient's arteries are irregularly shaped, highly tortuous and very narrow. The tortuous configuration of the arteries may present difficulties to a clinician in advancement of the balloon catheter to a treatment site. In addition, in some instances, the extent to which the lumen is narrowed at the treatment site is so severe that the lumen is completely or nearly completely obstructed, which may be described as a total occlusion. Total or near-total occlusions in arteries can prevent all or nearly all of the blood flow through the affected arteries. If the occlusion has been established for a long period of time, the lesion may be referred to as a chronic total occlusion or CTO. Chronic total occlusions can occur in coronary as well as peripheral arteries. Chronic total occlusions are often characterized by extensive plaque formation and typically include a fibrous cap surrounding softer plaque material. This fibrous cap may present a surface that is difficult to penetrate with a conventional medical guidewire.
A number of devices have been developed and/or used for the percutaneous interventional treatment of CTOs, such as stiffer guidewires, low-profile balloons, laser light emitting wires, atherectomy devices, drills, drug eluting stents, and re-entry catheters. The factor that is most determinative of whether the interventionalist can successfully recannalize a CTO is the interventionalist's ability to advance a suitable guidewire from a position within the true lumen of the artery proximal to the CTO lesion, across the CTO lesion, i.e., either through the lesion or around it, and then back into the true lumen of the artery at a location distal to the CTO lesion.
In some cases, such as where the artery is totally occluded by hard, calcified atherosclerotic plaque, the guidewire may tend to deviate to one side and penetrate through the intima of the artery, thereby creating a neo-lumen called a “subintimal tract” i.e., a penetration tract formed within the wall of the artery between the intima and adventitia. In these cases, the distal end of the guidewire may be advanced to a position distal to the lesion but remains trapped within the subintimal tract. In such instances, it is then necessary to divert or steer the guidewire from the subintimal tract back into the true lumen of the artery at a location distal to the CTO lesion. The process of manipulating the guidewire to reenter the artery lumen is often difficult and solutions have been proposed utilizing various means for dealing with such a problem.
A number of catheter-based devices have been heretofore useable to redirect subintimally trapped guidewires back into the true lumen of the artery. Included among these are a variety of catheters having laterally deployable cannulae, i.e., hollow needles. These catheters are advanced into the subintimal tract over the subintimally trapped guidewire, and the laterally deployable cannula is advanced from the catheter into the true lumen of the blood vessel, downstream of the CTO. A second guidewire is then passed through the laterally deployed cannula and is advanced into the true lumen of the artery. The laterally deployed cannula is then retracted into the catheter and the catheter is removed, along with the original guidewire, leaving just the second guidewire in place. This second guidewire is then useable to facilitate enlargement i.e., balloon dilation, atherectomy, etc., and/or stenting of the subintimal tract, thereby creating a subintimal reentry conduit around the CTO. Commercially available catheters of this type have been used successfully in the treatment of CTOs in relatively large vessels, such as the femoral artery, popliteal artery, etc. For example, the PIONEER® catheter system by Medtronic, Inc. utilizes a penetrator that exits through a side exit port of the catheter to puncture the intimal layer distal of the CTO to re-enter the true lumen of the vessel. However, their use in smaller diameter vessels, i.e., coronary arteries or below-the-knee applications, has been limited to date due to their relatively large diameter. Accordingly, there exists a need in the art for a low profile device and method of using such for treatment of a CTO in smaller diameter vessels, such as those located below the knee of a patient.